1. Field of the Invention
The present invention relates to a reflective liquid crystal display apparatus.
2. Description of the Related Art
A configuration is discussed in U.S. Pat. No. 5,327,270 to improve contrast of a reflective liquid crystal display apparatus. The configuration includes a polarization beam splitter used as both a polarizer and an analyzer, and a quarter wave plate, where the quarter wave plate is disposed in an optical path of light exiting the polarization beam splitter and being cast into the polarization beam splitter again, such that the fast axis or the slow axis thereof is substantially orthogonal to a plane containing the incident optical axis and reflected optical axis of the polarization beam splitter.
The configuration of a conventional example of a reflective liquid crystal display apparatus is illustrated in FIG. 40.
Reference numeral 22 denotes a polarization beam splitter, 25 denotes a quarter wave plate, 34 denotes a reflective liquid crystal display device, 28 denotes the fast axis of the quarter wave plate 25, 53 denotes an incident light ray, 54 denotes a reflected light ray, 55 denotes the polarization axis direction of the incident light ray 53 being cast into the quarter wave plate 25, and 56 denotes the polarization axis of the reflected light ray 54 which has transmitted through the quarter wave plate 25.
The incident light ray 53 is linear polarized light being cast into the quarter wave plate 25, and the reflected light ray 54, which has passed through the quarter wave plate 25 twice via the reflective liquid crystal display device 36, is also linear polarized light. The direction bisecting the polarization direction 55 of the incident light ray 53 and the polarization direction 56 of the reflected light ray 54 matches the fast axis 28. The polarization direction 56 of the reflected light ray 54 matches the S-polarization direction of the reflected light ray 54. The polarization beam splitter is designed to not facilitate transmission of s-polarized light, and thus there is no polarization component of the reflected light ray 54 that passes through the polarization beam splitter 22. Thus, increasing the incident angle range to the polarization beam splitter 22 does not lead to reduction in contrast.
Also, a configuration is discussed in U.S. Pat. No. 6,501,523 to improve contrast of a reflective liquid crystal display apparatus, where a reflective liquid crystal display apparatus comprises a reflective liquid crystal display device having a liquid crystal layer held between a transparent electrode and a reflecting electrode and a plurality of pixel circuits for driving the liquid crystal layer, and a wave plate, with the position of the optical axis (fast axis or slow axis) of the wave plate and the polarization direction of the incident polarized light with respect to the wave plate being slightly offset.
The configuration of a conventional example of a reflective liquid crystal display apparatus is illustrated in FIG. 41.
Reference numeral 101 denotes incident light, 102 denotes a polarization beam splitter, 103 denotes a polarizing film, 104 denotes a wave plate, 105 denotes an axis parallel to the polarization plane of S-polarized light, 106 denotes an axis parallel to the polarization plane of P-polarized light, 107 denotes a slow axis, 108 denotes a fast axis, 158 denotes a reflective liquid crystal display device, and 124 denotes the optical axis rotation angle of the wave plate.
Also, FIG. 42 illustrates reflectivity wavelength scattering properties in an arrangement where the optical axis rotation angle 124 (FIG. 41) of the quarter wave plate 104 is taken as a parameter with a TN (Twisted Nematic) mode twist angle of 80° and voltage of 4 Vrms applied for liquid crystal black display. Now, the optical axis rotation angle 124 of the quarter wave plate 104 is defined as θp, and increasing θp, with a θp=0 reference, reduces the reflectivity for liquid crystal black display. Particularly, taking note of the region around the wavelength 550 nm which is the center of the visible range and which greatly influences contrast, the reflectivity for liquid crystal black display is minimal when θp=around 3, i.e., contrast is increased.
Generally, with a liquid crystal display device used in liquid crystal projectors, pixels are arrayed in matrix fashion, and light cast into the liquid crystal display device exhibits diffraction and interference due to the shape of the pixel openings.
Also, the intensity of diffracted light is inversely proportionate to the size of the openings which have a cyclic structure, and also is proportionate to the wavelength. The pixel shape of liquid crystal devices for liquid crystal projectors is around 10 μm×10 μm, which is far smaller than those of direct-view liquid crystal devices used with personal computers, thus the diffraction phenomena occurs profusely. Moreover, diffracted (interference) light is reflected (transmitted) at a different angle from that of the specular reflection (0th order transmission), so phase difference error occurs due to liquid crystal wavelengths, outside the intended liquid crystal design values, passing through, resulting in reduced image quality of the image displayed.
The conventional art make no mention of diffracted light generated at the reflective liquid crystal display device, and thus they have not discussed that abnormal polarized light due to diffracted light cannot be controlled easily and that contrast cannot be sufficiently improved.